Vocabulary Generation:
The vocabulary consisting of \(K=256\)  visual words is computed from all SURF descriptors on Paris dataset. Various different cluster initializations of \(k\) -means are executed and the best clustering is used as the vocabulary for all evaluations. As the number of extracted descriptors is typically much larger than \(K\) , e.g. even the smallest Holidays dataset contains 8.3 million SURF descriptors. This vocabulary can be considered independent from all datasets. Such simplification has been used in literature [1]}. For every dataset, this vocabulary is used as a reference vocabulary and a vocabulary adaptation is performed as described in section REF .
